I jab constantly in boxing and it serves me well.
But when I throw out even a few jabs in MMA, I regret it.
A sole jab requires a step forward that stops.
Alot of guys in RMA respond to a jab by unloading a serious of blows.
In boxing gloves I can take their flurry and come back.
But in MMA, I wind up like Tito when Lidell unleashed.
You just can't let a man in Vale Tudo gloves come forward exploding on you.
I haven't seen anyone in my school use the jab effectively in my MMA school.Including us guys that use it well in boxing.

I think one of the reasons jabs work so well in boxing is the huge-ass gloves.

Jab towards the face, standard cover puts the gloves up in the line of sight, hard to see what's happening next.

Jab at someone wearing small gloves and they'll likely cover forward or counter right away, without the blinding from the gloves.

I respect the jab, we practice a rear cross over the jab as a standard counter but it certainly doesn't always work. I think its place in more realistic combat is much more limited than in boxing with 16 oz gloves, no kicks (hence forward stance), etc.

Jab with a simultaneous forward push kick to just above the knee...anyone else like this one?

I would liken it to the boxing or the muay thai of internal kung fu, even though that's like calling apples the oranges of the apple world. --WalkOn

As useful as the jab is, it, like any head punch, cna be difficult if your opponent is 7 foot(unless you are also about that height) and you are something like 5'6". HE would have to crouch down(which I doubt would happen as he would be inclined to boot you in the head) for you to reach him. You would have better luck doing the solar plexus routine w/said jab, or placing a foot wher it shoudn't go. Not that that scenario happens as most 7 footers are basketball players or professional wrestlers and fight each other.